Pebble shader in cycles
Here is what I came up with:

It is mostly procedural, I did use an image texture for the grooves but you could take that out and use a voroni texture (I just liked the way the texture looked).

If you are trying to make a ground plane with thousands of pebbles I would NOT go this route. I would use a pebble texture and use displacement. However if you are going for a close up pebble shot this shader should work well. 




The trick is to build up the layers of detail. 

The main left box is the main rock color, It is just broken up with a noise texture and 3 different colors. Use the color ramp to clamp the pattern.

*Notice I put a hue/saturation node (highlighted) I did this to quickly change the color of different rocks (or you could just change the 3 original colors).

The middle and front box are just for the scratches and grooves in the rock. The most important part here is to use the texture as a bump with a different color and material for the chipped grooves. 


I added in a texture and mapping node to just change the look of the textures across the different rocks (So they don't all look the same).